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Concentration of feldspar from trachyte
Published in Gülhan Özbayoğlu, Çetin Hoşten, M. Ümit Atalay, Cahit Hiçyılmaz, A. İhsan Arol, Mineral Processing on the Verge of the 21st Century, 2017
Mineralogical examinations of the sample revealed that 15% of the sample was phenocrystals of sanidine growing up to 2 cm in size. Body of the sample contained albite and biotite micro crystals as well The total alkali grade (Na2O + K2O) in hand picked (under microscope) phenocrystals of sanidine from the sample was around 13.30%.
Dating the Acraman asteroid impact, South Australia: the case for deep drilling the ‘hot shock’ zone of the central uplift
Published in Australian Journal of Earth Sciences, 2021
A dyke of melt rock in shattered dacite near the centre of Acraman consists mostly of slender, twinned skeletal laths of albite up to 350 × 20 µm, displaying radial quench textures, set in a matrix of finely intergrown K-feldspar and quartz with scattered grains of iron oxide (Figure 3d) (Timms et al., 2017; Williams, 1994). Patches of partly melted dacite show microcrystalline aggregates of quartz and K-feldspar. The form and composition of the feldspar laths suggests original high-temperature sanidine that crystallised rapidly from the melt. The glass matrix devitrified mostly to K-feldspar. Electron microprobe analyses indicate that the Na- and K-feldspar phases have essentially pure, end-member compositions: Ab99, 0.12 ± 0.05% K2O (±1σ), 10.53 ± 0.50% Na2O, 0.09 ± 0.08% CaO; and Or98, 15.57 ± 0.53% K2O, 0.32 ± 0.19% Na2O (Williams, 1994). Hence the feldspars are secondary, low-temperature phases (Boles, 1982; Kastner & Siever, 1979).
Petrogenetic links between the Dunedin Volcano and peripheral volcanics of the Karitane Suite
Published in New Zealand Journal of Geology and Geophysics, 2018
Oliver E. McLeod, James D. L. White
Feldspar compositions span from moderately calcic to strongly sodic plagioclase to alkali feldspar (Figure 8B). Groundmass microlites in basanite range from An46–62 and plot within the labradorite field. In trachyandesite, phenocrysts are zoned and range from An17–23 and plot just outside of the oligoclase field due to their potassic (Or8–15) compositions. Core compositions range from An19–27 and the first zone rims show variable, small fluctuations in An and Ab content. The second rims (outermost zones) show increased Or contents up to about 11 mol%. In phonolite, the main feldspar composition is sanidine (Or38–54). Trace element contents are illustrated in plots H and I of Figure 9. Strontium contents of feldspar (H) are highest in trachyandesite (0.30–0.63 wt%), slightly lower in basanite (0.18–0.5 wt%), and < 0.1 wt% in phonolite. One feldspar in phonolite has similar CaO and Sr content to those in trachyandesite. Barium contents of feldspar show similar variation across the three rock groups of up to at least 0.25 wt %. The highest contents are in trachyandesite (0.09–0.36 wt%) whereas most feldspars in basanite and phonolite contain ≤ 0.15 wt% BaO.